Ac generator sensor-less vector control method and control device thereof

ABSTRACT

It is the objective of the present invention to provide a sensorless vector control method and a control apparatus, for an alternating-current motor, that can smoothly restart an alternating-current motor in the free running state.  
     According to the present invention, when a current that flows in an alternating-current motor ( 2 ) at a restart time  7  the alternating-current motor ( 2 ) continuously flows at a designated current level or higher for a designated period of time, it is determined that the rotational direction or the velocity of the alternating-current motor ( 2 ) is incorrectly estimated, and a direct current or a direct-current voltage is again applied to again estimate the rotational direction and the velocity.

TECHNICAL FIELD

The present invention relates to a sensorless vector control method, foran alternating-current motor, whereby, before an alternating-current isstarted, the velocity of the alternating-current motor in the freerunning state is estimated and the alternating-current motor is operatedat the estimated velocity to provide a smooth start, and to a controlapparatus therefor.

BACKGROUND ART

Submitted by the present inventor and described in JP-A-2001-161094 is acontrol method, for an alternating-current motor, whereby are provided apower converter, for outputting power to the alternating-current motor,and a current controller, for controlling the current output by thepower converter based on a signal indicating a deviation between acurrent instruction signal and a detection signal indicating the currentoutput by the power converter, and whereby a velocity detector and avoltage detector are not provided. According to this control method,provided are the power converter, for outputting power to thealternating-current motor, and the power controller, for controlling thecurrent output by the power converter based on a signal indicating adeviation between a current instruction signal and a detection signalindicating the current output by the power converter, and when thealternating-current motor is in the free running state, an arbitrarydirect current is supplied for a designated period of time, a frequencycomponent that appears in the detection signal for the power output bythe power converter is detected, and the velocity of thealternating-current motor is estimated based on the frequency component.

Also disclosed is a control method whereby, when an alternating-currentmotor is in the free running state, a current instruction signaldescribed above is forcibly set to zero so as to adjust to zero thecurrent for the alternating-current motor; and whereby the level of theremaining voltage, the phase and the angular velocity of thealternating-current motor are obtained based on an output voltageinstruction signal that is obtained by using a calculation employing thecurrent output by the current controller, and then, the rotationaldirection and the velocity of the alternating-current motor in the freerunning state are estimated, so that the alternating-current motor canbe smoothly started in the free running state.

Furthermore, disclosed is a control method whereby, when an outputvoltage instruction signal, which is obtained by using a calculationbased on the output of the current controller when the current controlis performed with a current instruction signal of zero, is lower than anarbitrarily designated voltage level, the current control is halted andan instruction for a direct current having an arbitrary level istransmitted in an arbitrary direction for a designated period of time,and thereafter, an instruction for a current having an arbitrary levelis transmitted in a direction for which the phase differs by 180° fromthe direction in which the direct current instruction is transmitted;whereby the current control is again performed for a designated periodof time, and the frequency component that appears in the detectedcurrent value and the phase relationship are detected; and whereby thefrequency component is estimated to be the velocity of thealternating-current motor and the rotational direction is estimatedbased on the phase relationship.

However, according to the method described in JP-2001-161094, when aresidual high voltage remains in the alternating-current motor, avelocity differing greatly from the actual velocity of thealternating-current motor would be estimated to be due to the averseaffect of the residual voltage. In this case, when thealternating-current motor is started while a frequency corresponding tothe estimated velocity is designated for the power converter, a largecurrent flows that produces a velocity near the velocity erroneouslydetected for the alternating-current motor, and the alternating-currentmotor can not smoothly be restarted.

When a response from the current controller is not satisfactory, it isdifficult for the current of the alternating-current motor to be set tozero, the power converter falls into an overcurrent state, and thealternating-current motor can not smoothly be started.

Further, when the alternating-current motor is an induction motor, it iseasy for the current of the induction motor to be reduced to zerobecause the residual voltage in the free running state is graduallyreduced. But when the alternating-current motor is a permanent magnetsynchronous motor, a high inductive voltage is generated in the freerunning state at a high velocity, and it is not easy for the current ofthe permanent magnet synchronous motor to be set to zero.

Furthermore, when the alternating-current motor is in the free runningstate at a high velocity, the detection resolution for a frequency thatappears in a detected current value, or the amplitude of the signal of afrequency component that appears in a detected current value is reduced,so that the frequency can not be detected.

In addition, according to the control method for an alternating-currentmotor described in JP-A-2001-161094, when the alternating-current motoris in the free running state, an arbitrary direct current is suppliedfor a designated period of time. However, no specific explanation isgiven for the method for determining the designated period of time.

According to a control method for an alternating-current motor describedin Japanese Patent Application No. 2002-80891, a predesignated frequencyand a rotational direction that is detected are set for a frequencyadjustment circuit, and when an input torque current detection value ispositive, the output frequency is lowered, or when the torque currentdetection value is negative, the output frequency is increased. When theoutput frequency is adjusted in this manner, so that it nears the torquecurrent detection value of 0, the output frequency of thealternating-current motor in the free running state can match the outputfrequency of the power converter, so that a smooth start is obtained.

However, in this case also, the alternating-current motor is not alwayssmoothly restarted, even though the output frequency is adjusted so thatit nears the torque current detection value of 0.

Therefore, in order to resolve these shortcomings, it is a firstobjective of the present invention to provide a sensorless vectorcontrol method for an alternating-current motor, whereby when a wrongrotational direction or a wrong velocity is estimated when restartingthe alternating-current motor in the free running state, this can bedetermined to be an erroneous estimate and the alternating-current motorin the free running state can be smoothly restarted, and whereby when analternating-current motor in the free running state is to be restarted,a period for the application of a direct current to thealternating-current motor is correctly designated, so that thealternating-current motor in the free running state can be smoothlyrestarted; and a control apparatus therefor.

It is a second objective of the present invention to provide asensorless vector control method for an alternating-current motor,whereby a running operation can still be smoothly and appropriatelycontinued when a response by a current controller is poor, or when thealternating-current motor is an induction alternating-current motor, oreven a permanent magnet synchronous alternating-current motor; and acontrol apparatus therefor.

It is a third objective of the present invention to provide a sensorlessvector control method for an alternating-current motor, whereby thefollowing three points can be satisfied: when, after a currentinstruction signal is set to zero in order to adjust the current for thealternating-current motor to zero, current control is implemented toincrease the response of a current controller and to avoid the entryinto an overcurrent state of a power converter, so that the run-timeoperation can be smoothly continued; when, after an estimated velocityand rotational direction for the alternating-current motor are employedto provide a direct-current instruction for the alternating-currentmotor, the accuracy of the detection of a frequency is increased for thealternating-current motor in the free running state at a high velocity;and when the run-time operation continues smoothly even while thealternating-current motor is in the free running state at a highvelocity; and to provide a control apparatus therefor.

DISCLOSURE OF THE INVENTION

To achieve the above objectives, according to claim 1 of the presentinvention, a sensorless vector control method for an alternating-currentmotor,

-   -   the sensorless vector control method employing:    -   a power converter, for outputting arbitrary power to the        alternating-current motor,    -   a current detection circuit, for detecting a current supplied to        the alternating-current motor,    -   a coordinate conversion circuit, for converting the current        supplied to the alternating-current motor into an exciting        current detection value and a torque current detection value and        for outputting the exciting current detection value and the        torque current detection value,    -   an exciting current control circuit, for controlling an exciting        current directional voltage so as to match the exciting current        instruction value with the exciting current detection value,    -   a torque current control circuit, for controlling a torque        current directional voltage so as to match the toque current        instruction value with the torque current detection value,    -   a V/f conversion circuit, for calculating an induction voltage        for the alternating-current motor based on a given output        frequency instruction,    -   a phase angle operation circuit, for obtaining a phase angle by        integrating the given output frequency instruction, and    -   an output voltage operation circuit, for calculating a level and        a phase for an output voltage based on voltage instructions that        are output by the exciting current control circuit, the torque        current control circuit and the V/f conversion circuit, wherein    -   a phase angle, output by the phase angle operation circuit, is        added to the level and the phase output by the output voltage        operation circuit in order to regulate the switching of the        power converter, and    -   a velocity detector and a voltage detector are not provided, and    -   whereby a direct current or a direct-current voltage is applied        to the alternating-current motor in a free running state before        the alternating-current motor is started,    -   a rotational direction and a velocity for the        alternating-current motor are estimated based on a secondary        current that flows at the application time,    -   a frequency that corresponds to the rotational direction and the        velocity are set for a frequency adjustment circuit to activate        the alternating-current motor, and    -   the frequency adjustment circuit matches an output frequency        with the velocity of the alternating-current motor, is        characterized by:    -   estimating, based on the level of a current flowing in the        alternating-current motor, that the rotational direction and the        frequency designated for the frequency adjustment circuit        deviate from the actual rotational direction and the actual        velocity of the alternating-current motor.

According to claim 2 of the invention, the sensorless vector controlmethod for an alternating-current motor, described in claim 1, ischaracterized in that

-   -   a case that the level of the current flowing in the        alternating-current motor is continued for a designated period        of time, at an equal to or higher than designated current level,        is established as a reference that is used to estimate that the        rotational direction and the frequency designated for the        frequency adjustment circuit deviate from the actual rotational        direction and the actual velocity of the alternating-current        motor.

According to claim 3 of the invention, the sensorless vector controlmethod for an alternating-current motor, cited in claim 1 or 2, ischaracterized by:

-   -   after it is estimated that the rotational direction and the        frequency designated to the frequency adjustment circuit deviate        from the actual rotational direction and the actual velocity of        the alternating-current motor;    -   halting a restarting of the alternating-current motor;    -   applying a direct current or a direct-current voltage to the        alternating-current motor;    -   employing a secondary current, flowing at the application time,        to estimate, again, the rotational direction and the velocity of        the alternating-current motor; and    -   setting again, to the frequency adjustment circuit, a frequency        that corresponds to the rotational direction and the velocity,        and    -   restarting the alternating-current motor.

According to claim 4 of the invention, the sensorless vector controlmethod for an alternating-current motor, cited in claim 3, ischaracterized by:

-   -   when a direct current or a direct-current voltage is applied to        the alternating-current motor, and a secondary current flowing        at the application time is employed to reevaluate the rotational        direction and the velocity of the alternating-current motor,    -   while the velocity is estimated such that the upper limit value        for an estimated value is lower by a designated velocity value        than the velocity is previously estimated to be, or is equal to        the final output value of the frequency adjustment circuit; and    -   a frequency that corresponds to the estimated value is set to        the frequency adjustment circuit, and    -   the alternating-current motor is started.

According to claim 5 of the invention, a sensorless vector controlapparatus, for an alternating-current motor, including:

-   -   a power converter, for outputting arbitrary power to the        alternating-current motor,    -   a current detection circuit, for detecting a current supplied to        the alternating-current motor,    -   a coordinate conversion circuit, for converting the current        supplied to the alternating-current motor into an exciting        current detection value and a torque current detection value and        for outputting the exciting current detection value and the        torque current detection value,    -   an exciting current control circuit, for controlling an exciting        current directional voltage so as to match the exciting current        instruction value with the exciting current detection value,    -   a torque current control circuit, for controlling a torque        current directional voltage so as to match the toque current        instruction value with the torque current detection value,    -   a V/f conversion circuit, for calculating an induction voltage        for the alternating-current motor based on a given output        frequency instruction,    -   a phase angle operation circuit, for obtaining a phase angle by        integrating the given output frequency instruction, and    -   an output voltage operation circuit, for calculating a level and        a phase for an output voltage based on voltage instructions that        are output by the exciting current control circuit, the torque        current control circuit and the V/f conversion circuit, wherein    -   a phase angle, output by the phase angle operation circuit, is        added to the level and the phase output by the output voltage        operation circuit in order to regulate the switching of the        power converter,    -   a velocity detector and a voltage detector are not provided, and    -   a direct current or a direct-current voltage is applied to the        alternating-current motor in a free running state before the        alternating-current motor is started, a rotational direction and        a velocity for the alternating-current motor are estimated based        on a secondary current that flows at the application time, a        frequency that corresponds to the rotational direction and the        velocity are set for a frequency adjustment circuit to activate        the alternating-current motor, and the frequency adjustment        circuit matches an output frequency with the velocity of the        alternating-current motor, is characterized by including:    -   erroneous setup estimation member for estimating, based on the        level of a current flowing in the alternating-current motor,        that the rotational direction and the frequency designated for        the frequency adjustment circuit deviate from the actual        rotational direction and the actual velocity of the        alternating-current motor.

According to claim 6 of the invention, the sensorless vector controlapparatus for an alternating-current motor, described in claim 5, ischaracterized in that

-   -   a case that the level of the current flowing in the        alternating-current motor is continued for a designated period        of time, at an equal to or higher than designated current level,        is established as a reference that is used by the erroneous        setup estimation member to estimate that the rotational        direction and the frequency designated for the frequency        adjustment circuit deviate from the actual rotational direction        and the actual velocity of the alternating-current motor.

According to claim 7 of the invention, the sensorless vector controlapparatus for an alternating-current motor, cited in claim 5 or 6, ischaracterized by:

-   -   after the erroneous setup estimation member estimates a setup is        incorrect,    -   a restarting of the alternating-current motor is halted;    -   a direct current or a direct-current voltage is again applied to        the alternating-current motor;    -   a secondary current, flowing at the application time, is        employed to reevaluate the rotational direction and the velocity        of the alternating-current motor; and    -   a frequency that corresponds to the rotational direction and the        velocity is again set to the frequency adjustment circuit, and    -   the alternating-current motor is restarted.

According to claim 8 of the invention, the sensorless vector controlapparatus for an alternating-current motor, cited in claim 7, ischaracterized by:

-   -   when a direct current or a direct-current voltage is applied to        the alternating-current motor, and a secondary current flowing        at the application time is employed to reevaluate the rotational        direction and the velocity of the alternating-current motor,    -   while estimating the velocity is such that the upper limit value        for an estimated value is lower by a designated velocity value        than the velocity is previously estimated to be, or is equal to        the final output value of the frequency adjustment circuit; and    -   a frequency that corresponds to the estimated value and starting        the alternating-current motor is set for the frequency        adjustment circuit.

According to claim 9 of the invention, a sensorless vector controlmethod for an alternating-current motor, employing:

-   -   the sensorless vector control method employing:    -   a power converter, for outputting arbitrary power to the        alternating-current motor,    -   a current detection circuit, for detecting a current supplied to        the alternating-current motor,    -   a coordinate conversion circuit, for converting the current        supplied to the alternating-current motor into an exciting        current detection value and a torque current detection value and        for outputting the exciting current detection value and the        torque current detection value,    -   an exciting current control circuit, for controlling an exciting        current directional voltage so as to match the exciting current        instruction value with the exciting current detection value,    -   a torque current control circuit, for controlling a torque        current directional voltage so as to match the toque current        instruction value with the torque current detection value,    -   a V/f conversion circuit, for calculating an induction voltage        for the alternating-current motor based on a given output        frequency instruction,    -   a phase angle operation circuit, for obtaining a phase angle by        integrating the given output frequency instruction, and    -   an output voltage operation circuit, for calculating a level and        a phase for an output voltage based on voltage instructions that        are output by the exciting current control circuit, the torque        current control circuit and the V/f conversion circuit, wherein    -   a phase angle, output by the phase angle operation circuit, is        added to the level and the phase output by the output voltage        operation circuit in order to regulate the switching of the        power converter,    -   a velocity detector and a voltage detector are not provided,    -   whereby a direct current or a direct-current voltage is applied        to the alternating-current motor in a free running state before        the alternating-current motor is started,    -   a rotational direction and a velocity for the        alternating-current motor are estimated based on a secondary        current that flows at the application time,    -   a frequency that corresponds to the rotational direction and the        velocity are set for a frequency adjustment circuit to activate        the alternating-current motor, and    -   the frequency adjustment circuit matches an output frequency        with the velocity of the alternating-current motor, is        characterized by:    -   setting, as a period of time for applying a direct current or a        direct-current voltage, a greater value, either an estimated        lower limit value for the alternating-current motor, or a value        obtained based on a value designated as a secondary circuit time        constant.

According to claim 10 of the invention, the sensorless vector controlmethod for an alternating-current motor, cited in claim 9, ischaracterized by:

-   -   when the frequency of a secondary current is not obtained during        the period in which the direct current or the direct-current        voltage is being applied,    -   it is determined that the alternating-current motor is halted;        and    -   a predesignated lowest frequency or a zero frequency is        transmitted to the frequency adjustment circuit.

According to claim 11 of the present invention, a sensorless vectorcontrol apparatus, for an alternating-current motor, including:

-   -   a power converter, for outputting arbitrary power to the        alternating-current motor,    -   a current detection circuit, for detecting a current supplied to        the alternating-current motor,    -   a coordinate conversion circuit, for converting the current        supplied to the alternating-current motor into an exciting        current detection value and a torque current detection value and        for outputting the exciting current detection value and the        torque current detection value,    -   an exciting current control circuit, for controlling an exciting        current directional voltage so as to match the exciting current        instruction value with the exciting current detection value,    -   a torque current control circuit, for controlling a torque        current directional voltage so as to match the toque current        instruction value with the torque current detection value,    -   a V/f conversion circuit, for calculating an induction voltage        for the alternating-current motor based on a given output        frequency instruction,    -   a phase angle operation circuit, for obtaining a phase angle by        integrating the given output frequency instruction, and    -   an output voltage operation circuit, for calculating a level and        a phase for an output voltage based on voltage instructions that        are output by the exciting current control circuit, the torque        current control circuit and the V/f conversion circuit, wherein    -   a phase angle, output by the phase angle operation circuit, is        added to the level and the phase output by the output voltage        operation circuit in order to regulate the switching of the        power converter,    -   a velocity detector and a voltage detector are not provided, and    -   a direct current or a direct-current voltage is applied to the        alternating-current motor in a free running state for a set time        before the alternating-current motor is started,    -   a rotational direction and a velocity for the        alternating-current motor are estimated based on a secondary        current that flows at the application time,    -   a frequency that corresponds to the rotational direction and the        velocity are set for a frequency adjustment circuit to activate        the alternating-current motor,    -   the frequency adjustment circuit matches an output frequency        with the velocity of the alternating-current motor, is        characterized by:    -   setting, as a period of time for applying a direct current or a        direct-current voltage, a greater value, either an estimated        lower limit value for the alternating-current motor, or a value        obtained based on a value designated as a secondary circuit time        constant.

According to claim 12 of the invention, the sensorless vector controlapparatus for an alternating-current motor, cited in claim 11, ischaracterized by:

-   -   when the frequency of a secondary current is not obtained during        the period in which the direct current or the direct-current        voltage is being applied,    -   it is determined that the alternating-current motor is halted;        and    -   a predesignated lowest frequency or a zero frequency is        transmitted to the frequency adjustment circuit.

According to claim 13 of the invention, a sensorless vector controlmethod for an alternating-current motor,

-   -   the sensorless vector control method employing:    -   a power converter, for outputting power to an        alternating-current motor, and    -   a current controller, for controlling a current output by the        power converter based on a signal indicating a deviation between        a current instruction signal and a detection signal for a        current output by the power converter, wherein    -   a velocity detector and a voltage detector are not provided,    -   whereby current control is effected by forcibly setting the        current instruction signal to zero so as to reduce to zero a        current in the alternating-current motor in a free running        state, and    -   whereby a level and a phase of a residual voltage in the        alternating-current motor, and an angular velocity, are        calculated based on an output voltage instruction signal        obtained by employing a current output by the current        controller, and    -   a rotational direction and velocity of the alternating-current        motor in the free running state are estimated, is characterized        by:    -   determining a wait time until the current control is started        with the current instruction signal value set to zero in        accordance with a run-time frequency of the power converter        before the free running state and a secondary circuit time        constant of the alternating-current motor.

According to claim 14 of the invention, the sensorless vector controlmethod for an alternating-current motor, cited in claim 13, ischaracterized by:

-   -   when the run-time frequency of the power converter before the        free running state is entered is lower than an arbitrarily        designated frequency,    -   setting the wait time until the current control is started with        the current instruction signal value set to zero.

According to the claim 15 of the invention, for a sensorless vectorcontrol method for an alternating-current motor, the sensorless vectorcontrol method for an alternating-current motor, cited in claim 13 or14, is characterized by:

-   -   when an induction voltage of the alternating-current motor is so        high that it is difficult to adjust a current in the        alternating-current motor to zero,    -   halting the control for setting the current in the        alternating-current motor to zero;    -   permitting an arbitrarily provided time-power converter to        prepare switching so as to short-circuit three phases of an        input to the alternating-current motor,    -   exerting a damping force on the alternating-current motor;    -   decelerating the alternating-current motor;    -   controlling again, to zero, the current of the        alternating-current motor; and    -   estimating the rotational direction and the velocity of the        alternating-current motor in the free running state.

According to claim 16 of the invention, a sensorless vector controlapparatus for an alternating-current motor, including:

-   -   a power converter, for outputting power to an        alternating-current motor, and    -   a current controller, for controlling a current output by the        power converter based on a signal indicating a deviation between        a current instruction signal and a detection signal for a        current output by the power converter, wherein    -   a velocity detector and a voltage detector are not provided,    -   current control is effected by forcibly setting the current        instruction signal to zero so as to reduce to zero a current in        the alternating-current motor in a free running state, and    -   a level and a phase of a residual voltage in the        alternating-current motor, and an angular velocity, are        calculated based on an output voltage instruction signal        obtained by employing a current output by the current        controller, and    -   a rotational direction and velocity of the alternating-current        motor in the free running state are estimated, is characterized        by:    -   determining a wait time until the current control is started        with the current instruction signal value set to zero in        accordance with a run-time frequency of the power converter        before the free running state and a secondary circuit time        constant of the alternating-current motor.

According to claim 17 of the invention, the sensorless vector controlapparatus for an alternating-current motor, cited in claim 16, ischaracterized by:

-   -   when the run-time frequency of the power converter before the        free running state is entered is lower than an arbitrarily        designated frequency,    -   setting the wait time until the current control is started with        the current instruction signal value set to zero.

According to the claim 18 of the invention, for a sensorless vectorcontrol apparatus for an alternating-current motor, the sensorlessvector control apparatus for an alternating-current motor, cited inclaim 16 or 17, is characterized by:

-   -   when an induction voltage of the alternating-current motor is so        high that it is difficult to adjust a current in the        alternating-current motor to zero,    -   halting the control for setting the current in the        alternating-current motor to zero;    -   permitting an arbitrarily provided time-power converter to        prepare switching so as to short-circuit three phases of an        input to the alternating-current motor;    -   exerting a damping force on the alternating-current motor;    -   controlling again, to zero, the current of the        alternating-current motor that is decelerated; and    -   estimating the rotational direction and the velocity of the        alternating-current motor in the free running state.

According to claim 19 of the invention, a sensorless vector controlmethod for an alternating-current motor,

-   -   the sensorless vector control method employing:    -   a power converter, for outputting power to an        alternating-current motor, and    -   a current controller, for controlling a current output by the        power converter based on a signal indicating a deviation between        a current instruction signal and a detection signal for a        current output by the power converter, wherein    -   both a velocity detector and a voltage detector are not        provided,    -   whereby a current control is performed by forcibly setting the        current instruction signal to zero so as to reduce to zero a        current in the alternating-current motor in a free running        state, and    -   whereby a level and a phase of a residual voltage in the        alternating-current motor and an angular velocity are calculated        based on an output voltage instruction signal obtained by        employing a current output by the current controller, and then,    -   a rotational direction and a velocity of the alternating-current        motor in the free running state are estimated, is characterized        by:    -   when a process for reducing to zero the current in the        alternating-current motor is to be preformed,    -   reducing a scanning period for a current control process to less        than that for a normal control process.

According to claim 20 of the invention, the sensorless vector controlmethod for an alternating-current motor, cited in claim 19, ischaracterized by:

-   -   when the process for reducing to zero the current in the        alternating-current motor is to be preformed,    -   reducing the scanning period for the current control process to        less than that for the normal control process, as well as        increasing a carrier frequency of the power converter.

According to claim 21 of the invention, a sensorless vector controlapparatus for an alternating-current motor, including:

-   -   a power converter, for outputting power to an        alternating-current motor, and    -   a current controller, for controlling a current output by the        power converter based on a signal indicating a deviation between        a current instruction signal and a detection signal for a        current output by the power converter, wherein    -   a current control is performed by forcibly setting the current        instruction signal to zero so as to reduce to zero a current in        the alternating-current motor in a free running state,    -   a level and a phase of a residual voltage in the        alternating-current motor and an angular velocity are calculated        based on an output voltage instruction signal obtained by        employing a current output by the current controller, and then,    -   a rotational direction and a velocity of the alternating-current        motor in the free running state, and    -   both a velocity detector and a voltage detector are not        provided, is characterized by including:    -   member for, when a process for reducing to zero the current in        the alternating-current motor is to be preformed, reducing a        scanning period for a current control process to less than that        for a normal control process.

According to claim 22 of the invention, the sensorless vector controlapparatus for an alternating-current motor, cited in claim 21, ischaracterized by including:

-   -   member for, when the process for reducing to zero the current in        the alternating-current motor is to be preformed, reducing the        scanning period for the current control process to less than        that for the normal control process, as well as increasing a        carrier frequency of the power converter.

According to claim 23 of the invention, a sensorless vector controlmethod for an alternating-current motor,

-   -   the sensorless vector control method employing:    -   a power converter, for outputting power to an        alternating-current motor, and    -   a current controller, for controlling a current output by the        power converter based on a signal indicating a deviation between        a current instruction signal and a detection signal for a        current output by the power converter,    -   whereby current control is effected by forcibly setting the        current instruction signal to zero so as to reduce to zero a        current in the alternating-current motor in a free running        state,    -   whereby, when the current instruction signal, which is        calculated by using a current output by the current controller,        is lower than an arbitrarily designated voltage level,    -   current control is halted, and    -   a direct current instruction is transmitted at an arbitrary        level for a designated period of time,    -   whereby, thereafter, a current instruction is transmitted at an        arbitrary level in a direction with a phase 180° different from        the direction in which the direct-current voltage is        transmitted, and    -   the current control is performed again during a designated        period of time, and    -   whereby a velocity estimation circuit detects a frequency        component that appears in a current detection value and a phase        relationship thereof, estimates the frequency component as a        velocity of the alternating-current motor, and employs the phase        relationship to estimate a rotational direction of the        alternating-current motor,    -   both a velocity detector and a voltage detector are not        provided, is characterized by:    -   when the velocity and the rotational direction of the        alternating-current motor are estimated by providing a direct        current instruction for the alternating-current motor,    -   reducing a scanning time period for a current control process to        less than that for a normal control process.

According to claim 24 of the invention, the sensorless vector controlmethod for an alternating-current motor, cited in claim 23, ischaracterized by:

-   -   when the velocity and the rotational direction of the        alternating-current motor are estimated by providing a direct        current instruction for the alternating-current motor,    -   reducing a scanning period of time for a current control process        to less than that for a normal control process, as well as        increasing a carrier frequency of the power converter.

According to claim 25 of the invention, the sensorless vector controlmethod for an alternating-current motor, cited in claim 23 or 24, ischaracterized by:

-   -   when the velocity and the rotational direction of the        alternating-current motor are estimated by providing a direct        current instruction for the alternating-current motor,    -   reducing a scanning period of time for a current control process        to less than that for a normal control process, as well as        employing a current detector that is different from that used        for the normal control process and that is so sensitive a small        current is detected.

According to claim 26 of the invention, a sensorless vector controlapparatus for an alternating-current motor, including:

-   -   a power converter, for outputting power to an        alternating-current motor, and    -   a current controller, for controlling a current output by the        power converter based on a signal indicating a deviation between        a current instruction signal and a detection signal for a        current output by the power converter, wherein    -   current control is effected by forcibly setting the current        instruction signal to zero so as to reduce to zero a current in        the alternating-current motor in a free running state,    -   when the current instruction signal, which is calculated by        using a current output by the current controller, is lower than        an arbitrarily designated voltage level, current control is        halted, and a direct current instruction is transmitted at an        arbitrary level in an arbitrary direction for a designated        period of time,    -   thereafter, a current instruction is transmitted at an arbitrary        level in a direction with a phase 180° different from the        direction in which the direct-current voltage is transmitted,        and the current control is performed again during a designated        period of time, and    -   a velocity estimation circuit detects a frequency component that        appears in a current detection value and a phase relationship        thereof, estimates the frequency component as a velocity of the        alternating-current motor, and employs the phase relationship to        estimate a rotational direction of the alternating-current        motor, so that both a velocity detector and a voltage detector        are not provided, is characterized by including:    -   member for reducing a scanning time period for a current control        process to less than that for a normal control process when the        velocity and the rotational direction of the alternating-current        motor are estimated by providing a direct current instruction        for the alternating-current motor.

According to claim 27 of the invention, the sensorless vector controlapparatus for an alternating-current motor, cited in claim 26, ischaracterized by further including:

-   -   when the velocity and the rotational direction of the        alternating-current motor are estimated by providing a direct        current instruction for the alternating-current motor,    -   member for reducing a scanning period of time for a current        control process to less than that for a normal control process,        as well as increasing a carrier frequency of the power        converter.

According to claim 28 of the invention, the sensorless vector controlmethod for an alternating-current motor, cited in claim 26 or 27, ischaracterized by further including:

-   -   when the velocity and the rotational direction of the        alternating-current motor are estimated by providing a direct        current instruction for the alternating-current motor,    -   a current detector for reducing a scanning period of time for a        current control process to less than that for a normal control        process, as well as employing a current detector that is        different from that used for the normal control process and that        is so sensitive a small current is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a sensorlessvector control apparatus for an alternating-current motor according to afirst embodiment of the present invention;

FIG. 2 is a graph showing a change for a torque current detection valuei qfb for a case wherein a direct current is supplied to analternating-current motor, in the free running state, that is rotated inthe forward direction;

FIG. 3 is a graph showing a change for the torque current detectionvalue i qfb for a case wherein a direct current is supplied to thealternating-current motor, in the free running state, that is rotated inthe reverse direction;

FIG. 4 is a graph showing a change for the torque current detectionvalue i qfb for a case wherein a direct current is supplied to thealternating-current motor, in the free running state, that is rotated ata low velocity;

FIG. 5 is a graph showing a change for the torque current detectionvalue i qfb for a case wherein a direct current is supplied to thealternating-current motor that has a great secondary circuit timeconstant, as an example;

FIG. 6 is a flowchart showing the configuration according to the firstembodiment;

FIG. 7 is a block diagram showing the configuration of a sensorlessvector control apparatus for an alternating-current motor according to asecond embodiment of the present invention;

FIG. 8 shows an operation frequency before a free running state and await time until a restart occurs;

FIG. 9 is a block diagram showing the configuration of a sensorlessvector control apparatus for an alternating-current motor according to athird embodiment of the present invention; and

FIG. 10 is a block diagram showing the configuration of a sensorlessvector control apparatus for an alternating-current motor according to afourth embodiment of the present invention.

The reference numerals used in drawings are as follows:

-   -   1: power converter    -   2: alternating-current motor    -   3: current detector    -   4: current coordinates conversion circuit    -   5: torque current control circuit    -   6: exciting current control circuit    -   7: phase operation circuit    -   8: V/f conversion circuit    -   9: output voltage operation circuit    -   10: switching pattern generation circuit    -   11: frequency adjustment circuit    -   12, 13, 14, 17: switch    -   15: velocity estimation circuit (third embodiment)    -   15B: velocity estimation circuit (fourth embodiment)    -   16: adder

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will now be described while referring to thedrawings.

First, a first embodiment of the present invention will now beexplained.

According to the first embodiment, when an alternating-current motor isto be restarted, and when a current flowing in the alternating-currentmotor is continued at a designated current level or higher for adesignated period of time, it is determined that a rotational directionor a velocity is incorrectly estimated for the alternating-currentmotor, and a direct current or a direct-current voltage is applied againto estimate the rotational direction and the velocity.

FIG. 1 is a block diagram showing the configuration of a sensorlessvector control apparatus for an alternating-current motor according tothe first embodiment of the present invention. For this embodiment, thesensorless vector control apparatus for an alternating-current motorincludes: a power converter 1, an alternating-current motor 2, a currentdetector 3, a current coordinates conversion circuit 4, a torque currentcontrol circuit 5, an exciting current control circuit 6, a phaseoperation circuit 7, a V/f conversion circuit 8, an output voltageoperation circuit 9, a switching pattern generation circuit 10 and afrequency adjustment circuit 11.

The power converter 1 employs the PWM control system to convert, into analternating current having an arbitrary frequency and an arbitraryvoltage, a direct-current voltage obtained by converting a three-phasealternating current using a power device, and supplies the alternatingcurrent to the alternating-current motor 2.

The current detector 3 detects a current supplied to thealternating-current motor 2.

The current coordinates conversion circuit 4 splits the current detectedby the current detector 3 to obtain a torque current detection value iqfb and an exciting current detection value i dfb.

The torque current control circuit 5 calculates a first q-axial voltageinstruction value V′qref so that a provided torque current instructionvalue i qref matches the torque current detection value i qfb.

The exciting current control circuit 6 calculates ad-axial voltageinstruction value dref so that a provided exciting current instructionvalue i dref matches the exciting current detection value i dfb.

The phase operation circuit 7 integrates a provided frequency f1 toobtain a phase θ.

The V/f conversion circuit 8 employs the provided frequency f1 tocalculate a voltage Eref that corresponds to an induction voltage forthe alternating-current motor.

The output voltage operation circuit 9 obtains a second q-axial voltageinstruction Vqref by adding the first q-axial voltage instruction valueV′qref, which is the output of the torque current control circuit 5, tothe voltage Eref, which is the output of the V/f conversion circuit 8,and outputs an output voltage instruction value V1ref and its voltagephase θV in accordance with the second q-axial voltage instruction valueVqref and the d-axial voltage instruction value dref.

The switching pattern generation circuit 10 determines a switchingpattern for the power converter 1 based on the output voltageinstruction value V1ref and a power converter output phase θdeg, whichis obtained by adding the voltage phase θV and the phase θ.

The frequency adjustment circuit 11 is a circuit for adjusting thefrequency output by the power converter 1, so that the alternating-motorcurrent 2 in the free running state can be smoothly restarted.

For an estimation of the rotational direction and the velocity of thealternating-current motor 2 in the free running state, a direct currentinstruction is provided for the exciting current instruction value idref during an arbitrarily designated period of time, then, the currentcontrol is performed by changing the sign and the level of the directcurrent instruction and the change in the torque current detection valuei qfb is measured.

According to this invention, a direct current or a direct-currentvoltage is applied to the alternating-current motor in the free runningstate before it is restarted, and a secondary current that is flowing atthis time is employed to estimate the rotational direction and thevelocity of the alternating-current motor. In FIG. 2 is shown a casewherein the alternating-current motor 2 is rotated forward in the freerunning state, and in FIG. 3 is shown a case wherein thealternating-current motor 2 is rotated in reverse in the free runningstate. In FIGS. 2 and 3, (a) represents the exciting current detectionvalue i dfb of the alternating-current motor 2, and (b) represents atime-transient change of the torque current detection value i qfb of thealternating-current motor 2.

In FIG. 2, when at time t1 shown in (a) the exciting current detectionvalue i dfb having a negative rectangular wave is supplied to thealternating-current motor 2 that is rotated forward in the free runningstate, the torque current detection value i qfb having a waveform thatrises in the positive direction is produced, as is shown in (b).

On the other hand, as is shown in FIG. 3, when at time t1 in (a) theexciting current detection value i dfb having a negative rectangularwave is supplied to the alternating-current motor 2 that is rotated inreverse in the free running state, the torque current detection value iqfb having a waveform that falls in the negative direction is produced,also as is shown in (b).

By focusing on this point, the time-transient change of the obtainedtorque current detection value i qfb can be employed to detect therotational direction, and when the frequency of the torque currentdetection value i qfb is measured, the velocity of thealternating-current motor can be estimated.

The thus estimated rotational direction and velocity of thealternating-current motor 2 are set in the frequency adjustment circuit11, which is then operated. The frequency adjustment circuit 11 adjustsa frequency so that the torque current detection value i qfb reacheszero, and matches the velocity of the alternating-current motor 2 in thefree running state with the output frequency of the power converter.Thus, the alternating-current motor 2 can be smoothly started.

Furthermore, according to the present invention, when the estimatedvelocity value is wrong, or when the rotational direction is erroneouslydetected, this is automatically ascertained and a direct current isagain applied to estimate the rotational direction and the velocity ofthe alternating-current motor based on the time-transient change in thetorque current detection value i qfb. That is, it is assumed, inaccordance with the level of the current flowing in thealternating-current motor, that the rotational direction and thefrequency designated for the frequency adjustment circuit have deviatedfrom the actual rotational direction and the actual velocity of thealternating-current motor. Specifically, regarded as a necessarycondition is that the level of a current flowing in thealternating-current motor be continued, at a level equal to or higherthan the level of a designated current, for a designated period of time.When this condition is established, the restarting of thealternating-current motor is halted, a direct current or adirect-current voltage is again applied to the alternating-currentmotor, and a secondary current that is supplied at this time is employedto estimate again the rotational direction and the velocity of thealternating-current motor. For the re-estimation in this case, thevelocity is estimated so that the upper limit estimated value for thevelocity is lower by a designated velocity level than the previouslyestimated value, or is equal to the final output value of the frequencyadjustment circuit. Then, the frequency corresponding to the estimatedvalue is designated for the frequency adjustment circuit, and thealternating-current motor is started.

Next, while referring to FIGS. 1 and 6, a detailed explanation will begiven for the operation of the embodiment for restarting thealternating-current motor in the free running state.

When the alternating-current motor 2 is in the free running state, threeswitches S1 to S3 in FIG. 1 are changed from the normal running state ona side A to the free running start state on a side B. Therefore, thetorque current instruction value i qref=0 is established, an excitingcurrent instruction is output by the V/f conversion circuit 8, and theoutput frequency f1 is output by the frequency adjustment circuit 11. Itshould be noted that a zero frequency is set as an initial value for theoutput frequency adjustment circuit 11. Then, an arbitrary directcurrent (see (a) in FIG. 2 or 3) is supplied to the alternating-currentmotor 2 for a designated period of time (step S1). The detection value iqfb (see (b) in FIG. 2 or 3) for a torque current that is flowing atthis time is employed to estimate the frequency and the rotationaldirection (step S2). Based on the estimation results, the frequency andthe rotational direction are again designated for the output frequencyadjustment circuit 11 (step S3).

After the frequency and the rotational direction are again designatedfor the output frequency adjustment circuit 11, the V/f conversioncircuit 8 operates an exciting current instruction in accordance with asecondary circuit time constant so as to raise a magnetic flux, and themagnetic flux and the designated frequency f1 are employed to calculateand output the voltage Eref that corresponds to an induction voltage forthe alternating-current motor.

The frequency adjustment circuit 11 reduces the frequency when thetorque current detection value i qfb is positive, or increases theoutput frequency when the torque current detection value i qfb isnegative, so that the torque current detection value i qfb approaches 0.

When the magnetic flux has reached the level for normal operation, andwhen the torque current detection value i qfb reaches a specific setuplevel close to 0 (i.e., when the current flowing in thealternating-current motor is no longer continued at a setup level orhigher for an arbitrary period of time (NO at step S4)), it isdetermined that the alternating-current motor can be started normally,and the three switches S1 to S3 are switched to side A (step S7).

On the other hand, when, while the frequency adjustment circuit 11 isadjusting the frequency, the current flowing in the alternating-currentmotor is continued at an arbitrary setup level or higher for anarbitrary period of time (YES at step S4), it is determined in thisembodiment that an abnormal state has apparently occurred (step S5).This state is a case wherein either the rotational direction of thealternating-current motor differs from the rotational directiondesignated for the frequency adjustment circuit 11, or wherein thevelocity of the alternating-current motor deviates greatly from thefrequency setup value designated for the frequency adjustment circuit11.

When this state is detected, the power converter is temporarily halted(step S6), program control returns to step S1, whereat a direct currentis again applied, the rotational direction and the velocity of thealternating-current motor are estimated and again designated for thefrequency adjustment circuit.

In this case, a value obtained by subtracting an arbitrary level valuefrom the previously estimated frequency, or the last frequency output bythe frequency adjustment circuit, is defined as the upper limit for theestimated velocity value of the alternating-current motor. Then, anerroneous detection during re-evaluation can be prevented.

Furthermore, in this embodiment, an explanation is given for the powerconversion apparatus that splits the current flowing in thealternating-current motor 2 into a torque current and an excitingcurrent, and provides vector control for controlling these currentsindependently. However, the present invention can also be provided by apower conversion apparatus that provides constant V/f control byperforming exactly the same processing, so long as a current controlcircuit is additionally provided that applies a current flowing in thealternating-current motor in the free running state into a torquecurrent and an exciting current, and that controls these currentsindependently.

A modification of the first embodiment will now be described.

The modification of the first embodiment relates to a method for settingan arbitrary period of time during which a direct current instruction isprovided for the exciting current instruction value i dref. A greatervalue, either the lower limit value of the estimated velocity for thealternating-current motor or a secondary circuit time constant, isdesignated as an arbitrary period for applying a direct current in orderto correctly estimate the rotational direction and the velocity of thealternating-current motor.

As one method for measuring the frequency of a torque current detectionvalue, there is a method for measuring a cycle for a peak on thepositive side and a peak on the negative side, or a cycle between zerocross points.

However, when a cycle T1 between a peak on the positive side and a peakon the negative side or a cycle T2 between zero cross points, shown inFIG. 4, can not be measured, the frequency can not be detected.Therefore, a direct current must be continuously supplied to enable thedetection of the frequency.

Thus, the focus is that so long as the alternating-current motor is inthe free running state at a low velocity, the power converter can besmoothly activated, with little shock, even with the zero frequency orthe lowest frequency that can be output, and thus, the lower limit valueis designated in advance as the estimated velocity value for thealternating-current motor in the free running state. When the estimatedvelocity is lower than the lower limit value, it is determined that thealternating-current motor is halted, and the estimated velocity value isset as a predesignated value or a zero frequency for the frequencyadjustment circuit.

Further, for an alternating-current motor having a large secondarycircuit time constant, a case occurs wherein the torque currentdetection value i qfb has a waveform shown in FIG. 5, due to the affectof a residual voltage, and wherein a rotational direction can not beaccurately detected. In order to negate the affect of the residualvoltage, a direct current is applied during a period equivalent to, orproportional to, the secondary circuit time constant.

As a result, the residual voltage is canceled by the applied current,the waveform in FIG. 5 is changed to the waveform shown in FIG. 2 (orFIG. 3), which is easily deleted, and the rotational direction can beaccurately estimated.

Therefore, as the method for the setup of an arbitrary period wherein adirect current instruction is provided, a longer period is allocated,either a period obtained based on the predesignated lower limit valuefor the velocity estimated value, or a period equivalent to orproportional to the secondary circuit time constant.

Since the operation for restarting the alternating-current motor in thefree running state is described in detail in the first embodiment, noexplanation for it will be given here.

An explanation of the present invention is given for a power conversionapparatus that splits a current flowing in the alternating-current motor2 into a torque current and an exciting current, and that providesvector control for controlling these currents independently. However,the present invention can also be provided by a power conversionapparatus that provides constant V/f control by performing exactly thesame processing, so long as a current control circuit is additionallyprovided that splits a current flowing in the alternating-current motorin the free running state into a torque current and an exciting currentand that controls these currents independently.

Moreover, in the present invention, as the frequency measurement method,an explanation is given for the method used to measure a cycle between apeak on the positive side and a peak on the negative side, or a cyclebetween the zero cross points. However, the velocity of thealternating-current motor can also be estimated by using a commonfrequency detection method that is established.

FIG. 7 is a block diagram showing the configuration of a sensorlessvector control apparatus for an alternating-current motor according to asecond embodiment of the present invention. For this embodiment, thesensorless vector control apparatus for an alternating-current motorincludes: a power converter 1, an alternating-current motor 2, a currentdetector 3, a current coordinates conversion circuit 4, a torque currentcontrol circuit 5, an exciting current control circuit 6, a phaseoperation circuit 7, a V/f conversion circuit 8, an output voltageoperation circuit 9, a switching pattern generation circuit 10, switches12, 13 and 14 and a velocity estimation circuit 15.

The power converter 1 performs switching of a main circuit power device,and employs the PWM control system to convert, into an alternatingcurrent having an arbitrary frequency and an arbitrary voltage, adirect-current voltage obtained by forward conversion of a three-phasealternating current using a power device, and supplies the alternatingcurrent to the alternating-current motor 2. The current detector 3detects a current supplied to the alternating-current motor 2. Thecurrent coordinates conversion circuit 4 splits the current detected bythe current detector 3 to obtain a torque current detection value iqfband an exciting current detection value idfb. The torque current controlcircuit 5 calculates a first q-axial voltage instruction value V′qref sothat a provided torque current instruction value iqref matches thetorque current detection value iqfb. The exciting current controlcircuit 6 calculates a d-axial voltage instruction value dref so that aprovided exciting current instruction value idref matches the excitingcurrent detection value idfb.

The phase operation circuit 7 integrates a provided frequency f1 toobtain a phase θ. The V/f conversion circuit 8 employs the providedfrequency f1 to calculate a voltage Eref that corresponds to aninduction voltage for the alternating-current motor.

The output voltage operation circuit 9 obtains a second q-axial voltageinstruction Vqref by adding the first q-axial voltage instruction valueV′qref, which is the output of the torque current control circuit 5, tothe voltage Eref, which is the output of the V/f conversion circuit 8,and outputs an output voltage instruction value V1ref and its voltagephase θV in accordance with the second q-axial voltage instruction valueand the d-axial voltage instruction value. The switching patterngeneration circuit 10 determines a switching pattern for the powerconverter 1 based on the output voltage instruction value V1ref and apower converter output phase θdeg, which is obtained by adding thevoltage phase θV and the phase θ.

The velocity estimation circuit 15 is a circuit for estimating avelocity fr for the alternating-current motor 2 in the free runningstate. The switch 12 is a switch that switches the torque currentinstruction value iqref to a side B, which is zero, or to a side A,which is for the input to the torque current control circuit 5. Theswitch 13 is a switch for switching the exciting current instructionvalue idref to a side B, which is zero, or to a side A, which is for theinput to the exciting current control circuit 6. The switch 14 is aswitch that switches the frequency f1 to a side B, which is zero, or toa side A, which is for the input to the V/f conversion circuit 8.

A detailed explanation will now be given for the operation forrestarting the alternating-current motor in the free running state. Whenthe alternating-current motor 2 is in the free running state, the threeswitches 12, 13 and 14 in FIG. 7 are switched from the normal runningstate on the side A to the free-running start state on the side B. Then,the torque current instruction value iqref=0 and the exciting currentinstruction value idref=0 are established. Further, since a referencephase is not present because the alternating-current motor is in thefree running state, a phase that is to be added in accordance with theoutput frequency during the normal control is fixed at zero, and acurrent flowing in the alternating-current motor is adjusted to zero.Since an induction voltage is generated in accordance with therotational velocity of the alternating-current motor in the free runningstate, and is rotated at the rotational velocity of thealternating-current motor, a current is supplied between thealternating-current motor 2 and the power converter 1 when the powerconverter 1 is initiated, regardless of the levels of the rotationalvelocity and the induction voltage of the alternating-current motor 2.Therefore, the current must be adjusted to zero by the torque currentcontrol circuit 5 and the exciting current control circuit 6, so thatthe level of the induction voltage, the phase and the frequency of thealternating-current motor 2 match the level of the output voltage, thephase and the frequency of the power converter. Adjusting the currentflowing in the alternating-current motor to zero is called zero-currentcontrol.

A first q-axial voltage instruction value V′qref and ad-axial voltageinstruction value Vdref, which are the outputs of the torque currentcontrol circuit 5 and the exciting current control circuit 6 duringzero-current control, are voltage instruction values for which afrequency having a sine wave form is consonant with the rotationalvelocity of the alternating-current motor 2. The output voltageoperation circuit 9 receives the first q-axial voltage instruction valueV′qref and the d-axial voltage instruction value, and outputs the outputvoltage instruction value V1ref and the voltage phase θV. The outputvoltage instruction value V1ref represents the level of an inductionvoltage for the alternating-current motor, and the voltage phase θ0represents the phase of the induction voltage. When the time-transientchange in the phase of the induction voltage is measured for eachspecific period of time, the velocity estimation circuit 15 measures thefrequency of the induction voltage. Since, as is apparent from theprevious explanation, the frequency for the induction voltage matchesthe rotational velocity of the alternating-current motor 2, therotational velocity of the alternating-current motor 2 in the freerunning state can be estimated. When the alternating-current motor isrotated in reverse, the phase change ratio becomes negative, so that theforward rotation or the reverse rotation of the alternating-currentmotor in the free running state can also be estimated. As is describedabove, when the induction voltage of the alternating-current motor isobserved through zero-current control, not only the rotational directionbut also the rotational velocity of the alternating-current motor can beestimated.

An explanation will now be given for a method whereby an estimatedrotational direction and an estimated velocity are set for the powerconverter when zero-current control is switched to normal control. Whenthe power converter 1 is started by matching only the frequencies inorder to shift the zero-current control state to normal operation, anovercurrent may flow to the alternating-current motor and a smooth startmay not be obtained. In order to prevent this, the induction voltage atthe level during zero-current control and the phase must be continuedeven at the moment zero-current control is shifted to normal control.Therefore, the initial value must be set for the output voltageinstruction value v1ref, the output phase θdeg and the output frequencyf1 of the power converter. Specifically, in a normal operation state,the output phase θdeg of the power converter is adjusted by using thephase of the magnetic flux of the alternating-current motor 2 as areference, while in zero-current control, the output phase is the oneconsonant with the induction voltage of the alternating-current motor 2.As a result, during zero-current control, the phase for forward rotationis advanced 90° from the phase during normal control, and the phase forthe reverse rotation is delayed 90°. Therefore, in accordance with therotational direction, the phase is corrected by 90° from the last phasein the zero-current control, the estimated value fr, which is output bythe velocity estimation circuit 15 as the rotational velocity of thealternating-current motor 2, is converted into a phase, this obtainedphase is added to the corrected phase, and the resultant value is set asan initial value for the output phase θdeg of the power converter.Through this processing, continuity of the phase can be maintained.

Further, the output voltage instruction value V1ref, output duringzero-current control, is designated as an induction voltage, andcontinuity of the output voltage is maintained. Through this processing,zero-current control can be smoothly shifted to normal control.

As for an induction motor used as the alternating-current motor, sincean induction voltage is attenuated in accordance with the secondarycircuit time constant, it is determined, when the induction voltage hasreached the normal V/f level based on the secondary circuit timeconstant, that the alternating-current motor in the free running statecan be started normally, and the three switches 12, 13 and 14 areswitched to side A.

As for a permanent magnet synchronous motor that is used as thealternating-current motor, since an induction voltage is not attenuated,it is determined, when the process is completed for obtaining continuityfor the phase and the output voltage, that the alternating-current motorin the free running state can be normally started, and the threeswitches 12, 13 and 14 are switched to side A.

An explanation will now be given for a method for determining a waittime until the power converter is restarted. In order to estimate thevelocity of the alternating-current motor in the free running state, thefirst q-axial voltage instruction value V′qref and the d-axial voltageinstruction value Vdref, which are the outputs of the torque currentcontrol circuit 5 and the exciting current control circuit 6, must matchthe induction voltage of the alternating-current motor. This will not bea problem so long as the torque current control circuit 5 and theexciting current control circuit 6 demonstrate satisfactory functionsfor reducing the current flowing in the alternating-current motor tozero.

However, when the gains in the torque current control circuit 5 and theexciting current control circuit 6 are low, or when thealternating-current motor is rotated at a high velocity, a highinduction voltage occurs, and an excessive amount of current flowsimmediately after the power converter is started, so that the powerconverter may be tripped and may not be smoothly started. To preventthis, the response capabilities of the torque current control circuit 5and the exciting current control circuit 6 need only be obtained inadvance, and the voltage level generated by the alternating-currentmotor in the free running state need only be set equal to or lower thanan arbitrary value, so that zero-current control can be performed, andestimation of the velocity is enabled. That is, the induction voltage ofthe alternating-current motor need only be set equal to or lower than aarbitrarily designated voltage level.

This can be provided, as one method, by controlling the period of timebefore the power converter is restarted. Since the induction voltage ofthe alternating-current motor is determined based on a running timefrequency before the free running state, the wait time is not requiredwhen the operation is performed with a frequency at which the inductionvoltage is reduced until equal to or lower than the arbitrarilydesignated voltage level. When the operation is performed at thisfrequency or higher, the wait time is required, and can be obtained inaccordance with the running time frequency before the free running stateand the secondary circuit time constant of the alternating-currentmotor. When the maximum wait time required is calculated and obtained inaccordance with the secondary circuit time constant of thealternating-current motor, an appropriate wait time can be determined,as is shown in FIG. 8, in accordance with the running-time frequencybefore the alternating-current motor enters the free running state.

An explanation will now be given for a method according to anotherinvention for coping with a case wherein, since the induction voltage ofthe alternating-current motor is large, it is difficult for the currentin the alternating-current motor to be adjusted to zero. When thealternating-current motor is an induction motor having a large secondarycircuit time constant or a permanent magnet synchronous motor, there isa possibility that the induction voltage will not be reduced until equalto or lower than an arbitrarily designated voltage level, even when theabove described wait time has elapsed. In this case, zero-currentcontrol is temporarily halted, switching is performed for the powerconverter, so that the three phases of the alternating-current motor areshort-circuited, and the three-phase short circuit is continued for anarbitrarily designated period of time. Then, a damping force isgenerated in the alternating-current motor, which thereafterdecelerates.

Therefore, the induction voltage of the alternating-current motor isreduced. After an arbitrary period of time has elapsed, zero-currentcontrol is again initiated, and when the induction voltage is droppeduntil equal to or lower than the arbitrarily designated voltage level,the velocity can be estimated through zero-current control. However,when the induction voltage is not equal to or lower than the arbitrarilydesignated voltage level, the switching is again performed to maintainthe three-phase short circuit during the arbitrary period of time. As isdescribed above, it is characterized in that this process is repeateduntil the induction voltage of the alternating-current motor is reducedto the arbitrarily designated voltage level, so that the flow of anexcessive amount of current and the tripping of the power converter canbe prevented, and the alternating-current motor can be smoothlyrestarted.

Furthermore, in this embodiment, an explanation will be given for thepower conversion apparatus that splits a current flowing in thealternating-current motor 2 into a torque current and an excitingcurrent, and that provides vector control for controlling these currentsindependently. However, the present invention can also be provided by apower conversion apparatus that performs the constant V/f control byperforming exactly the same processing, so long as a current controlcircuit is additionally provided that splits a current flowing in thealternating-current motor in the free running state into a torquecurrent and an exciting current, and that controls these currentsindependently.

FIG. 9 is a block diagram showing the configuration of a sensorlessvector control apparatus for an alternating-current motor according to athird embodiment of the present invention.

For this embodiment, the sensorless vector control apparatus for analternating-current motor includes: a power converter 1, analternating-current motor 2, a current detector 3, a current coordinatesconversion circuit 4, a torque current control circuit 5, an excitingcurrent control circuit 6, a phase operation circuit 7, a V/f conversioncircuit 8, an output voltage operation circuit 9, a switching patterngeneration circuit 10, a velocity estimation circuit 15 and an adder 16.The power converter 1 employs the PWM control system to convert, into analternating current having an arbitrary frequency and an arbitraryvoltage, a direct-current voltage obtained by converting a three-phasealternating current using a power device, and supplies the alternatingcurrent to the alternating-current motor 2.

The current detector 3 detects a current supplied to thealternating-current motor 2, and supplies a current detection signal tothe current coordinates conversion circuit 4.

The current coordinates conversion circuit 4 splits the current detectedby the current detector 3 to obtain a torque current detection valueiqfb and an exciting current detection value idfb, transmits theobtained torque current detection value iqfb to the torque currentcontrol circuit 5, and transmits the obtained exciting current detectionvalue idfb to the exciting current control circuit 6. The torque currentcontrol circuit 5 calculates a first q-axial voltage instruction valueV′qref so that a provided torque current instruction value iqref matchesthe torque current detection value iqfb.

The exciting current control circuit 6 calculates ad-axial voltageinstruction value dref so that a provided exciting current instructionvalue idref matches the exciting current detection value idfb.

The phase operation circuit 7 integrates a provided frequency f1 toobtain a phase θ, and transmits the phase θ to the current coordinatesconversion circuit 4 and the adder 16.

The V/f conversion circuit 8 employs the provided frequency f1 tocalculate a voltage Eref that corresponds to an induction voltage forthe alternating-current motor. This voltage Eref is set in advance so asto establish Eref/f1=constant value.

The output voltage operation circuit 9 obtains a second q-axial voltageinstruction Vqref by adding the first q-axial voltage instruction valueV′qref, which is the output of the torque current control circuit 5, tothe voltage Eref, which is the output of the V/f conversion circuit 8,and outputs an output voltage instruction value V1ref and its voltagephase θV in accordance with the second q-axial voltage instruction valueVqref and the d-axial voltage instruction value dref.V 1 ref=[(Vdref)2+(Vqref)2]1/2  (1)θV=tan−1(Vqref/Vdref)  (2)

The switching pattern generation circuit 10 determines a switchingpattern for the power converter 1 based on the output voltageinstruction value V1ref and a power converter output phase θdeg, whichis obtained by adding the voltage phase θV and the phase θ.

The velocity estimation circuit 15 is a circuit that employs changes inthe voltage phase θV, by the unit hour, to estimate the velocity fr andthe rotational direction of the alternating-current motor 2 in the freerunning state.

A detailed explanation will now be given for the operation forrestarting the alternating-current motor in the free running state. Whenthe alternating-current motor 2 is in the free running state, the threeswitches 12, 13 and 14 in FIG. 9 are switched from the normal runningstate on the side A to the free-running start state on the side B. Then,the torque current instruction value iqref=0 and the exciting currentinstruction value idref=0 are established. Further, since a referencephase is not present because the alternating-current motor is in thefree running state, a phase that is to be added in accordance with theoutput frequency during the normal control is fixed at zero, and acurrent flowing in the alternating-current motor is adjusted to zero.Since an induction voltage is generated in accordance with therotational velocity of the alternating-current motor 2 in the freerunning state, and is rotated at the rotational velocity of thealternating-current motor, a current is supplied between thealternating-current motor 2 and the power converter 1 when the powerconverter 1 is initiated, regardless of the levels of the rotationalvelocity and the induction voltage of the alternating-current motor 2.Therefore, the current must be adjusted to zero by the torque currentcontrol circuit 5 and the exciting current control circuit 6, so thatthe level of the induction voltage, the phase and the frequency of thealternating-current motor 2 match the level of the output voltage, thephase and the frequency of the power converter. Adjusting the currentflowing in the alternating-current motor to zero is called zero-currentcontrol.

A first q-axial voltage instruction value V′qref and a d-axial voltageinstruction value Vdref, which are the outputs of the torque currentcontrol circuit 5 and the exciting current control circuit 6 duringzero-current control, are voltage instruction values for which afrequency having a sine wave form is consonant with the rotationalvelocity of the alternating-current motor 2. The output voltageoperation circuit 9 receives the first q-axial voltage instruction valueV′qref and the d-axial voltage instruction value Vdref, and outputs theoutput voltage instruction value V1ref and the voltage phase θV. Theoutput voltage instruction value V1ref represents the level of aninduction voltage for the alternating-current motor, and the voltagephase θ0 represents the phase of the induction voltage. When thetime-transient change in the phase of the induction voltage is measuredfor each specific period of time, the velocity estimation circuit 15measures the frequency of the induction voltage. Since, as is apparentfrom the previous explanation, the frequency for the induction voltagematches the rotational velocity of the alternating-current motor 2, therotational velocity in the free running state can be estimated. When thealternating-current motor is rotated in reverse, the phase change ratiobecomes negative, so that the forward rotation or the reverse rotationof the alternating-current motor in the free running state can also beestimated. As is described above, when the induction voltage of thealternating-current motor is observed through zero-current control, notonly the rotational direction but also the rotational velocity of thealternating-current motor can be estimated.

An explanation will now be given for a method whereby an estimatedrotational direction and an estimated velocity are set for the powerconverter when zero-current control is switched to normal control.

When the power converter 1 is started by matching only the frequenciesin order to shift the zero-current control state to normal operation, anovercurrent may flow to the alternating-current motor and a smooth startmay not be obtained. In order to prevent this, the induction voltage atthe level during zero-current control and the phase must be continuedeven at the moment zero-current control is shifted to normal control.Therefore, the initial value must be set for the output voltageinstruction value v1ref, the output phase θdeg and the output frequencyf1 of the power converter. Specifically, in a normal operation state,the output phase θdeg of the power converter is adjusted by using thephase of the magnetic flux of the alternating-current motor 2 as areference, while in zero-current control, the output phase is the oneconsonant with the induction voltage of the alternating-current motor 2.As a result, during zero-current control, the phase for forward rotationis advanced 90° from the phase during normal control, and the phase forthe reverse rotation is delayed 90°. Therefore, in accordance with therotational direction, the phase is corrected by 90° from the last phasein the zero-current control, the estimated value fr, which is output bythe velocity estimation circuit 15 as the rotational velocity of thealternating-current motor 2, is converted into a phase, this obtainedphase is added to the corrected phase, and the resultant value is set asan initial value for the output phase θdeg of the power converter.Through this processing, continuity of the phase can be maintained.

Further, the output voltage instruction value V1ref, output duringzero-current control, is designated as an induction voltage, andcontinuity of the output voltage is maintained. Through this processing,zero-current control can be smoothly shifted to normal control.

The induction voltage of the alternating-current motor is graduallyincreased in accordance with the secondary circuit time constant, andwhen the induction voltage matches the normal V/f level, it isdetermined that the alternating-current motor in the free running statecan be normally started, and the three switches are switched to the sideA.

An explanation will now be given for a method according to the presentinvention for improving current response during zero-current control. Inorder to estimate the velocity of the alternating-current motor in thefree running state, the first q-axial voltage instruction value V′qrefand the d-axial voltage instruction value Vdref, which are the outputsof the torque current control circuit 5 and the exciting current controlcircuit 6 during zero-current control, must match the induction voltageof the alternating-current motor.

This will not be a problem so long as the torque current control circuit5 and the exciting current control circuit 6 demonstrate satisfactoryfunctions for adjusting the current flowing in the alternating-currentmotor to zero. However, when the gains of the torque current controlcircuit 5 and the exciting current control circuit 6 can not beincreased, or when the alternating-current motor is rotated at a highvelocity, a high induction voltage is generated and an excessive amountof current flows immediately after the power converter is initiated, sothat the power converter may be tripped and may not be smoothly started.To prevent this, the responses of the torque current control circuit 5and the exciting current control circuit 6 must be improved. Sinceresponses are delayed when the scanning period for performing currentcontrol is short, the current can be controlled as instructed. So longas the other operations are omitted during zero-current control, thescanning period for current control can be reduced, compared with normalcontrol, and the current control response can be improved. Further, whenthe preparation of the switching pattern for the power converter isdelayed, even though the scanning period for current control is reducedduring zero-current control, the effects obtained by the reduction ofthe scanning period for current control are reduced by half. Therefore,when zero-current control is to be used, only a carrier frequency usedas a reference need be increased for the power converter to be operatedat a high velocity. In this manner, the current control response can beimproved.

As is described above, it is characterized in that the current controlscanning period during zero-current control is reduced compared withnormal control, or the carrier frequency for the power converter isincreased, so that the current control response is improved, the flow ofan excessive amount of current during zero-current control and thetripping of the power converter can be prevented, and thealternating-current motor can be smoothly restarted.

An explanation will now be given by referring to FIG. 10, which is ablock diagram showing the configuration of a sensorless vector controlapparatus for an alternating-current motor according to a modificationfor a fourth embodiment of the present invention.

The sensorless vector control apparatus for a motor according to thisembodiment includes: a power converter 1, an alternating-current motor2, a current detector 3, a current coordinates conversion circuit 4, atorque current control circuit 5, an exciting current control circuit 6,a phase operation circuit 7, a V/f conversion circuit 8, an outputvoltage operation circuit 9, a switching pattern generation circuit 10and a velocity estimation circuit 15B. Since the components other thanthe velocity estimation circuit 15B are employed in common, noexplanation for them will be given.

The velocity estimation circuit 15B is a circuit used to estimate thevelocity and the rotational direction of the alternating-current motor2, in the free running state, in accordance with a torque currentdetection value iqfb and an exciting current detection value idfbobtained upon the application of a direct current.

A detailed explanation will now be given for the operation forrestarting the alternating-current motor in the free running state. Inthe third embodiment, when an output voltage instruction value valueV1ref, which is output by the output voltage operation circuit 9 duringzero-current control, is lower than an arbitrarily designated level, itcan not be determined whether this has occurred because thealternating-current motor in the free running state is substantiallyhalted, or whether a residual voltage has dissipated due to a smallsecondary circuit time constant. Therefore, when this state occurs, theoperation in the third embodiment is halted, and a switch is made to theoperation in the fourth embodiment.

Three switches (12, 14 and 17) in FIG. 10 are switched from the normaloperation state on side A to the free-running start state on side B, andthus, a torque current instruction iqref=0 is established. Further,since no phase is used as a reference while the alternating-currentmotor is in the free running state, a phase to be added in accordancewith the output frequency during the normal control is fixed at zero,and a current flowing in the alternating-current motor is controlled. Inaddition, a second q-axial voltage instruction value Vqref is set tozero in order to employ the torque current detection value iqfb, for thealternating-current motor in the free running state, for estimating thevelocity and the rotational direction.

A specific setup value is provided as an exciting current instructionvalue idref in order to excite the alternating-current motor, and theexciting current control circuit 6 provides the control for a designatedperiod of time, so that an exciting current detection value idfb isequal to the exciting current instruction value idref. Thereafter, thesign and the level of the exciting current instruction value idref arechanged, and control is provided for a designated period of time.

At this time, by applying a direct current, a magnetic flux is generatedin the alternating-current motor in the free running state, so that asecondary current that temporarily flows across the rotor of thealternating-current motor is detected, based on the torque currentdetection value iqfb. The frequency of the torque current detectionvalue iqfb and the phase information obtained upon the application ofthe direct current are detected, and the velocity and the rotationaldirection of the alternating-current motor are estimated.

When the alternating-current motor 2 is rotated forward, the torquecurrent detection value iqfb is changed as is shown in FIG. 2. When thesign of the exciting current detection value idfb is negative, the phaseof the torque current detection value iqfb is changed to a sine wavebeginning at 0°. When the sign of the exciting current detection valueidfb is positive, the phase of the torque current detection value iqfbis changed to a sine wave beginning at 180°. Since the frequency of thesine wave of the torque current detection value iqfb matches thevelocity of the alternating-current motor 2 in the free running state,the velocity of the alternating-current motor 2 can be obtained bymeasuring the frequency of the torque current detection value iqfb.Furthermore, when the alternating-current motor is rotated in reverse,the torque current detection value iqfb is changed as is shown in FIG.3. When the sign of the exciting current detection value idgb isnegative, the phase of the torque current detection value iqfb ischanged to a sine wave beginning at 180°. When the sign of the excitingcurrent detection value idfb is positive, the phase of the toque currentdetection value iqfb is changed to a sine wave beginning at 0°.

As is described above, when a direct current is applied to thealternating-current motor, the phase relationship between the excitingcurrent detection value idfb and the torque current detection valueiqfb, and the frequency of the torque current detection value iqfb aredetected, so that the velocity and the rotational direction can beestimated.

An explanation will now be given for a method for designating, for thepower converter, a rotational direction and a velocity that areestimated when the direct current application state is shifted to normalcontrol after an arbitrary time has elapsed. In this case, unlike thethird embodiment, a magnetic flux must be newly generated because almostno induction voltage remains in the alternating-current motor, and thepower converter 1 need only be started by matching the rotationaldirection and the frequency. The induction voltage of thealternating-current motor is gradually increased in accordance with thesecondary circuit time constant, and when the induction voltage reachesthe normal V/f level, it is determined that the alternating-currentmotor in the free running state can be normally started, and the threeswitches are switched to side A.

An explanation will now be given for a method according to the inventionfor increasing the accuracy whereby a velocity is estimated by detectingthe frequency of the torque current detection value iqfb during theapplication of a direct current.

When the alternating-current motor is in the free running state at ahigh velocity, the frequency of the torque current detection value igfbin FIG. 2 or 3 is increased. As one method for measuring the frequencyof the torque current detection value iqfb, there is a method formeasuring the cycle between a peak on the positive side and a peak onthe negative side, or the cycle between zero cross points. When thescanning for current control is slow to measure the cycle between a peakon the positive side and a peak on the negative side, or the cyclebetween zero cross points, the accuracy of the measurement of the cycleis low, and the accuracy of the detection of the frequency is also low.Further, when the alternating-current motor is in the free running stateat a high velocity, a difference between a direct current and thefrequency of the alternating-current motor is increased, and because ofthis frequency difference, the impedance is increased while a currentflowing in the rotor is reduced. Accordingly, the torque currentdetection value iqfb is reduced, and it is difficult to measure thecycle between the peak on the positive side and the peak on the negativeside of the torque current detection value iqfb, or the cycle betweenzero cross points.

So long as other operations are omitted during the application of thedirect current, the scanning period for current control can be reduced,compared with during normal control, and the frequency detectionaccuracy can be increased. Furthermore, when the current controlscanning period is reduced during the application of the direct currentand the carrier frequency of the power converter is increased, thecurrent control response can be improved, and the exciting currentdetection value idfb can be adjusted to provide a rectangular waveform.Therefore, the secondary current of the alternating-current motor iscompletely reflected onto the torque current detection value iqfb. Inaddition, when the velocity of the alternating-current motor in the freerunning state is increased, the torque current detection value igfb isreduced, and detection is difficult using a common current detectionmethod. Therefore, during the application of the direct current, thedetection sensitivity of the current detection circuit need only beincreased several times to detect even a small current, so that, in thefree running state at a high velocity, the cycle between the peak on thepositive side and the peak on the negative side, or the cycle betweenthe zero cross points, can be measured.

It is, therefore, characterized in that: the current control responsecan be improved by reducing the current control scanning period duringthe application of a direct current, and by increasing the carrierfrequency of the power converter; the velocity of thealternating-current motor in the free running state can be accuratelymeasured since the resolution is increased for the measurement of thecycle between the positive-side peak and the negative-side peak of thetorque current detection value iqfb, or the cycle between zero crosspoints; and since during the application of a direct current thedetection sensitivity of the current detection circuit is increased morethan when under normal control, the velocity can be detected in the freerunning state under a restriction, so that the alternating-current motorcan be smoothly restarted.

Moreover, according to this embodiment, an explanation is given for apower conversion apparatus that splits a current flowing in thealternating-current motor 2 into a torque current and an excitingcurrent, and provides vector control for controlling these currentsindependently. However, the present invention can also be provided by apower conversion apparatus that performs the constant V/f control byperforming exactly the same processing, so long as a current controlcircuit is additionally provided that splits a current flowing in thealternating-current motor in the free running state into a torquecurrent and an exciting current and that controls these currentsindependently.

The present invention is described in detail by referring to specificembodiments. However, it will be obvious for one having ordinary skillin the art that the present invention can be variously modified oraltered without departing from the spirit and the scope of theinvention.

The present application is based on Japanese Patent Application (No.2002-198712) filed on Jul. 8, 2002, Japanese Patent Application (No.2002-315177) filed on Oct. 30, 2002 and Japanese Patent Application (No.2003-121733) filed on Apr. 25, 2003, and the contents of theseapplications are employed here as references.

INDUSTRIAL APPLICABILITY

As is described above, according to the first embodiment of the presentinvention, when the alternating-current motor is restarted and thecurrent continuously flows in the alternating-current motor at adesignated current level or higher for a designated period of time, itis determined that the rotational direction or the velocity of thealternating-current motor is incorrectly estimated, and a direct currentor a direct-current voltage is again applied to estimate the rotationaldirection and the velocity. Therefore, the alternating-current motor inthe free running state can be smoothly restarted.

According to the modification of the first embodiment of the presentinvention, since a greater value, either the lower limit value of theestimated velocity of the alternating-current motor or the secondarycircuit time constant, is designated as an arbitrary period for theapplication of a direct current, the optimal direct current applicationtime is employed to appropriately estimate the rotational direction andthe velocity of the alternating-current motor. Therefore, thealternating-current motor in the free running state can also be smoothlyrestarted.

According to the second embodiment of the invention, a sensorless vectorcontrol method for an alternating-current motor,

-   -   whereby there are provided a power converter, for outputting        power to an alternating-current motor, and a current controller,        for controlling an output current of the power converter based        on a signal indicating a deviation between a current instruction        signal and a detection signal for an output current of the power        converter, and a velocity detector and a voltage detector are        not provided,    -   whereby current control is performed by forcibly setting the        current instruction signal to zero so as to reduce to zero a        current in the alternating-current motor in a free running        state,    -   whereby a level and a phase of a remaining voltage in the        alternating-current motor and an angular velocity are calculated        based on an output voltage instruction signal obtained by        employing a current output by the current controller, and a        rotational direction and a velocity of the alternating-current        motor in the free running state are estimated, and    -   whereby, in accordance with a running frequency of the power        converter before the free running state, and a secondary circuit        time constant of the alternating-current motor, determining a        wait time until the current control is started with the current        instruction signal set to zero. Therefore, a control method and        a control apparatus for an alternating-current motor can be        provided whereby, when the response from the current controller        is poor, or when not only an induction motor but also a        permanent magnet synchronous motor is employed as the        alternating-current motor, the operation of the        alternating-current motor can be appropriately and smoothly        continued.

According to the third embodiment of the invention, when the currentcontrol is performed by forcibly setting the current instruction signalto zero in order to reduce the current at the alternating-current motorto zero, the response from the current controller is increased, theovercurrent state of the power converter is avoided, and the operationcan be smoothly continued.

According to the fourth embodiment of the invention, when the velocityand the rotational direction of the alternating-current motor in thefree running state at a high velocity are estimated by providing adirect current instruction, the accuracy of the detection of thefrequency is increased. Thus, effects can be obtained such that theoperation can be smoothly continued when the alternating-current motoris in the free running state at a high velocity.

1. A sensorless vector control method for an alternating-current motor,the sensorless vector control method employing: a power converter, foroutputting arbitrary power to the alternating-current motor, a currentdetection circuit, for detecting a current supplied to thealternating-current motor, a coordinate conversion circuit, forconverting the current supplied to the alternating-current motor into anexciting current detection value and a torque current detection valueand for outputting thereof, an exciting current control circuit, forcontrolling an exciting current directional voltage so as to match theexciting current instruction value with the exciting current detectionvalue, a torque current control circuit, for controlling a torquecurrent directional voltage so as to match the toque current instructionvalue with the torque current detection value, a V/f conversion circuit,for calculating an induction voltage for the alternating-current motorbased on a given output frequency instruction, a phase angle operationcircuit, for obtaining a phase angle by integrating the given outputfrequency instruction, and an output voltage operation circuit, forcalculating a level and a phase for an output voltage based on voltageinstructions that are output by the exciting current control circuit,the torque current control circuit and the V/f conversion circuit,wherein a velocity detector and a voltage detector are not provided, aphase angle, output by the phase angle operation circuit, is added tothe level and the phase output by the output voltage operation circuitin order to regulate the switching of the power converter, thesensorless vector control method comprising the steps of: applying adirect current or a direct-current voltage to the alternating-currentmotor in a free running state before the alternating-current motor isstarted, estimating a rotational direction and a velocity for thealternating-current motor based on a secondary current that flows at theapplication time, setting a frequency that corresponds to the rotationaldirection and the velocity for a frequency adjustment circuit toactivate the alternating-current motor, matching the frequencyadjustment circuit an output frequency with the velocity of thealternating-current motor, and estimating, based on the level of acurrent flowing in the alternating-current motor, that the rotationaldirection and the frequency designated for the frequency adjustmentcircuit deviate from the actual rotational direction and the actualvelocity of the alternating-current motor.
 2. The sensorless vectorcontrol method for an alternating-current motor, according to claim 1,wherein a case that the level of the current flowing in thealternating-current motor is continued for a designated period of time,at an equal to or higher than designated current level, is establishedas a reference that is used to estimate that the rotational directionand the frequency designated for the frequency adjustment circuitdeviate from the actual rotational direction and the actual velocity ofthe alternating-current motor.
 3. The sensorless vector control methodfor an alternating-current motor, according to claim 1, wherein after itis estimated that the rotational direction and the frequency designatedto the frequency adjustment circuit deviate from the actual rotationaldirection and the actual velocity of the alternating-current motor, arestarting of the alternating-current motor is halted, a direct currentor a direct-current voltage is applied to the alternating-current motor,a secondary current, flowing at the application time, is employed toreevaluate the rotational direction and the velocity of thealternating-current motor, a frequency that corresponds to therotational direction and the velocity is again set to the frequencyadjustment circuit, and the alternating-current motor is restarted. 4.The sensorless vector control method for an alternating-current motor,according to claim 3, wherein when a direct current or a direct-currentvoltage is applied to the alternating-current motor, and a secondarycurrent flowing at the application time is employed to reevaluate therotational direction and the velocity of the alternating-current motor,the velocity is estimated that the upper limit value for an estimatedvalue is lower by a designated velocity value than the velocity ispreviously estimated to be, or is equal to the final output value of thefrequency adjustment circuit, a frequency that corresponds to theestimated value is set to the frequency adjustment circuit, and thealternating-current motor is started.
 5. A sensorless vector controlapparatus, for an alternating-current motor, comprising: a powerconverter, for outputting arbitrary power to the alternating-currentmotor, a current detection circuit, for detecting a current supplied tothe alternating-current motor, a coordinate conversion circuit, forconverting the current supplied to the alternating-current motor into anexciting current detection value and a torque current detection valueand for outputting thereof, an exciting current control circuit, forcontrolling an exciting current directional voltage so as to match theexciting current instruction value with the exciting current detectionvalue, a torque current control circuit, for controlling a torquecurrent directional voltage so as to match the toque current instructionvalue with the torque current detection value, a V/f conversion circuit,for calculating an induction voltage for the alternating-current motorbased on a given output frequency instruction, a phase angle operationcircuit, for obtaining a phase angle by integrating the given outputfrequency instruction, and an output voltage operation circuit, forcalculating a level and a phase for an output voltage based on voltageinstructions that are output by the exciting current control circuit,the torque current control circuit and the V/f conversion circuit,wherein a phase angle, output by the phase angle operation circuit, isadded to the level and the phase output by the output voltage operationcircuit in order to regulate the switching of the power converter, avelocity detector and a voltage detector are not provided, and a directcurrent or a direct-current voltage is applied to thealternating-current motor in a free running state before thealternating-current motor is started, a rotational direction and avelocity for the alternating-current motor are estimated based on asecondary current that flows at the application time, a frequency thatcorresponds to the rotational direction and the velocity are set for afrequency adjustment circuit to activate the alternating-current motor,and the frequency adjustment circuit matches an output frequency withthe velocity of the alternating-current motor, the sensorless vectorcontrol apparatus, further comprising: erroneous setup estimation memberfor estimating, based on the level of a current flowing in thealternating-current motor, that the rotational direction and thefrequency designated for the frequency adjustment circuit deviate fromthe actual rotational direction and the actual velocity of thealternating-current motor.
 6. The sensorless vector control apparatusfor an alternating-current motor, according to claim 5, wherein a casethat the level of the current flowing in the alternating-current motoris continued for a designated period of time, at an equal to or higherthan designated current level, is established as a reference that isused by the erroneous setup estimation member to estimate that therotational direction and the frequency designated for the frequencyadjustment circuit deviate from the actual rotational direction and theactual velocity of the alternating-current motor.
 7. The sensorlessvector control apparatus for an alternating-current motor, according toclaim 5, wherein after the erroneous setup estimation member estimates asetup is incorrect, a restarting of the alternating-current motor ishalted, a direct current or a direct-current voltage is again applied tothe alternating-current motor, a secondary current, flowing at theapplication time, is employed to reevaluate, the rotational directionand the velocity of the alternating-current motor, a frequency thatcorresponds to the rotational direction and the velocity is again set tothe frequency adjustment circuit, and the alternating-current motor isrestarted.
 8. The sensorless vector control method for analternating-current motor, according to claim 7, wherein when a directcurrent or a direct-current voltage is applied to thealternating-current motor, and a secondary current flowing at theapplication time is employed to reevaluate the rotational direction andthe velocity of the alternating-current motor, while estimating thevelocity is such that the upper limit value for an estimated value islower by a designated velocity value than the velocity is previouslyestimated to be, or is equal to the final output value of the frequencyadjustment circuit, and a frequency that corresponds to the estimatedvalue and starting the alternating-current motor is set for thefrequency adjustment circuit.
 9. A sensorless vector control method foran alternating-current motor, the sensorless vector control methodemploying: a power converter, for outputting arbitrary power to thealternating-current motor, a current detection circuit, for detecting acurrent supplied to the alternating-current motor, a coordinateconversion circuit, for converting the current supplied to thealternating-current motor into an exciting current detection value and atorque current detection value and for outputting thereof, an excitingcurrent control circuit, for controlling an exciting current directionalvoltage so as to match the exciting current instruction value with theexciting current detection value, a torque current control circuit, forcontrolling a torque current directional voltage so as to match thetoque current instruction value with the torque current detection value,a V/f conversion circuit, for calculating an induction voltage for thealternating-current motor based on a given output frequency instruction,a phase angle operation circuit, for obtaining a phase angle byintegrating the given output frequency instruction, and an outputvoltage operation circuit, for calculating a level and a phase for anoutput voltage based on voltage instructions that are output by theexciting current control circuit, the torque current control circuit andthe V/f conversion circuit, wherein a phase angle, output by the phaseangle operation circuit, is added to the level and the phase output bythe output voltage operation circuit in order to regulate the switchingof the power converter, a velocity detector and a voltage detector arenot provided, the sensorless vector control method comprising the stepsof: applying a direct current or a direct-current voltage to thealternating-current motor in a free running state for a set time beforethe alternating-current motor is started, estimating a rotationaldirection and a velocity for the alternating-current motor based on asecondary current that flows at the application time, setting afrequency that corresponds to the rotational direction and the velocityfor a frequency adjustment circuit to activate the alternating-currentmotor, and matching the frequency adjustment circuit an output frequencywith the velocity of the alternating-current motor, and setting, as aperiod of time for applying a direct current or a direct-currentvoltage, a greater value, either an estimated lower limit value for thealternating-current motor, or a value obtained based on a valuedesignated as a secondary circuit time constant.
 10. The sensorlessvector control method for an alternating-current motor, according toclaim 9, wherein when the frequency of a secondary current is notobtained during the period in which the direct current or thedirect-current voltage is being applied, it is determined that thealternating-current motor is halted, and a predesignated lowestfrequency or a zero frequency is transmitted to the frequency adjustmentcircuit.
 11. A sensorless vector control apparatus, for analternating-current motor, comprising: a power converter, for outputtingarbitrary power to the alternating-current motor, a current detectioncircuit, for detecting a current supplied to the alternating-currentmotor, a coordinate conversion circuit, for converting the currentsupplied to the alternating-current motor into an exciting currentdetection value and a torque current detection value and for outputtingthereof, an exciting current control circuit, for controlling anexciting current directional voltage so as to match the exciting currentinstruction value with the exciting current detection value, a torquecurrent control circuit, for controlling a torque current directionalvoltage so as to match the toque current instruction value with thetorque current detection value, a V/f conversion circuit, forcalculating an induction voltage for the alternating-current motor basedon a given output frequency instruction, a phase angle operationcircuit, for obtaining a phase angle by integrating the given outputfrequency instruction, and an output voltage operation circuit, forcalculating a level and a phase for an output voltage based on voltageinstructions that are output by the exciting current control circuit,the torque current control circuit and the V/f conversion circuit,wherein a phase angle, output by the phase angle operation circuit, isadded to the level and the phase output by the output voltage operationcircuit in order to regulate the switching of the power converter, avelocity detector and a voltage detector are not provided, a directcurrent or a direct-current voltage is applied to thealternating-current motor in a free running state for a set time beforethe alternating-current motor is started, a rotational direction and avelocity for the alternating-current motor are estimated based on asecondary current that flows at the application time, a frequency thatcorresponds to the rotational direction and the velocity are set for afrequency adjustment circuit to activate the alternating-current motor,the frequency adjustment circuit matches an output frequency with thevelocity of the alternating-current motor, and a greater value, eitheran estimated lower limit value for the alternating-current motor, or avalue obtained based on a value designated as a secondary circuit timeconstant is set as a period of time for applying a direct current or adirect-current voltage.
 12. The sensorless vector control apparatus foran alternating-current motor, according to claim 11, wherein when thefrequency of a secondary current is not obtained during the period inwhich the direct current or the direct-current voltage is being applied,it is determined that the alternating-current motor is halted, and apredesignated lowest frequency or a zero frequency is transmitted to thefrequency adjustment circuit.
 13. A sensorless vector control method foran alternating-current motor, the sensorless vector control methodemploying: a power converter, for outputting power to analternating-current motor, and a current controller, for controlling acurrent output by the power converter based on a signal indicating adeviation between a current instruction signal and a detection signalfor a current output by the power converter, wherein a velocity detectorand a voltage detector are not provided, the sensorless vector controlmethod comprising the steps of: effecting current control by forciblysetting the current instruction signal to zero so as to reduce to zero acurrent in the alternating-current motor in a free running state,calculating a level and a phase of a residual voltage in thealternating-current motor, and an angular velocity, based on an outputvoltage instruction signal obtained by employing a current output by thecurrent controller, estimating a rotational direction and velocity ofthe alternating-current motor in the free running state, and determininga wait time until the current control is started with the currentinstruction signal value set to zero in accordance with a run-timefrequency of the power converter before the free running state and asecondary circuit time constant of the alternating-current motor. 14.The sensorless vector control method for an alternating-current motor,according to claim 13, wherein when the run-time frequency of the powerconverter before the free running state is entered is lower than anarbitrarily designated frequency, the wait time until the currentcontrol is started with the current instruction signal value of zero isset to zero.
 15. The sensorless vector control method for analternating-current motor, according to claim 13 or 14, wherein when aninduction voltage of the alternating-current motor is so high that it isdifficult to adjust a current in the alternating-current motor to zero,the control for setting the current in the alternating-current motor tozero is halted, an arbitrarily provided time-power converter ispermitted to prepare switching so as to short-circuit three phases of aninput to the alternating-current motor, a damping force on thealternating-current motor is exerted, the alternating-current motor isdecelerated, the current of the alternating-current motor is controlledagain to zero, and the rotational direction and the velocity of thealternating-current motor in the free running state are estimated.
 16. Asensorless vector control apparatus for an alternating-current motor,comprising: a power converter, for outputting power to analternating-current motor, and a current controller, for controlling acurrent output by the power converter based on a signal indicating adeviation between a current instruction signal and a detection signalfor a current output by the power converter, wherein a velocity detectorand a voltage detector are not provided, current control is effected byforcibly setting the current instruction signal to zero so as to reduceto zero a current in the alternating-current motor in a free runningstate, and a level and a phase of a residual voltage in thealternating-current motor, and an angular velocity, are calculated basedon an output voltage instruction signal obtained by employing a currentoutput by the current controller, a rotational direction and velocity ofthe alternating-current motor in the free running state are estimated,and a wait time until the current control is started with the currentinstruction signal value set to zero is determined in accordance with arun-time frequency of the power converter before the free running stateand a secondary circuit time constant of the alternating-current motor.17. The sensorless vector control apparatus for an alternating-currentmotor, according to claim 16, wherein when the run-time frequency of thepower converter before the free running state is entered is lower thanan arbitrarily designated frequency, the wait time until the currentcontrol is started with the current instruction signal value set to zerois set.
 18. The sensorless vector control apparatus for analternating-current motor, according to claim 16, wherein when aninduction voltage of the alternating-current motor is so high that it isdifficult to adjust a current in the alternating-current motor to zero,the control for setting the current in the alternating-current motor tozero is halted, an arbitrarily provided time-power converter ispermitted to prepare switching so as to short-circuit three phases of aninput to the alternating-current motor, a damping force on thealternating-current motor is exerted, the alternating-current motor isdecelerated, the current of the alternating-current motor is controlledagain to zero, and the rotational direction and the velocity of thealternating-current motor in the free running state is estimated.
 19. Asensorless vector control method for an alternating-current motor,employing: a power converter, for outputting power to thealternating-current motor, and a current controller, for controlling acurrent output by the power converter based on a signal indicating adeviation between a current instruction signal and a detection signalfor a current output by the power converter, wherein both a velocitydetector and a voltage detector are not provided, the sensorless vectorcontrol method comprising the steps of: performing a current control byforcibly setting the current instruction signal to zero so as to reduceto zero a current in the alternating-current motor in a free runningstate, and calculating a level and a phase of a residual voltage in thealternating-current motor and an angular velocity based on an outputvoltage instruction signal obtained by employing a current output by thecurrent controller, and estimating a rotational direction and a velocityof the alternating-current motor in the free running state, thesensorless vector control method further comprising the step of: when aprocess for reducing to zero the current in the alternating-currentmotor is to be preformed, reducing a scanning period for a currentcontrol process to less than that for a normal control process.
 20. Thesensorless vector control method for an alternating-current motor,according to claim 19, wherein when the process for reducing to zero thecurrent in the alternating-current motor is to be preformed, thescanning period for the current control process is reduced to less thanthat for the normal control process, as well as a carrier frequency ofthe power converter is increased.
 21. A sensorless vector controlapparatus for an alternating-current motor, comprising: a powerconverter, for outputting power to an alternating-current motor, and acurrent controller, for controlling a current output by the powerconverter based on a signal indicating a deviation between a currentinstruction signal and a detection signal for a current output by thepower converter, wherein a current control is performed by forciblysetting the current instruction signal to zero so as to reduce to zero acurrent in the alternating-current motor in a free running state, alevel and a phase of a residual voltage in the alternating-current motorand an angular velocity are calculated based on an output voltageinstruction signal obtained by employing a current output by the currentcontroller, and then, a rotational direction and a velocity of thealternating-current motor in the free running state are estimated, andboth a velocity detector and a voltage detector are not provided, thesensorless vector control apparatus further comprising: member for, whena process for reducing to zero the current in the alternating-currentmotor is to be preformed, reducing a scanning period for a currentcontrol process to less than that for a normal control process.
 22. Thesensorless vector control apparatus for an alternating-current motor,according to claim 21, further comprising: member for, when the processfor reducing to zero the current in the alternating-current motor is tobe preformed, reducing the scanning period for the current controlprocess to less than that for the normal control process, as well asincreasing a carrier frequency of the power converter.
 23. A sensorlessvector control method for an alternating-current motor, the sensorlessvector control method employing: a power converter, for outputting powerto an alternating-current motor, and a current controller, forcontrolling a current output by the power converter based on a signalindicating a deviation between a current instruction signal and adetection signal for a current output by the power converter, thesensorless vector control method comprising the steps of: effectingcurrent control by forcibly setting the current instruction signal tozero so as to reduce to zero a current in the alternating-current motorin a free running state, when the current instruction signal, which iscalculated by using a current output by the current controller, is lowerthan an arbitrarily designated voltage level, halting current control,transmitting a direct current instruction at an arbitrary level for adesignated period of time, thereafter transmitting a current instructionat an arbitrary level in a direction with a phase 180° different fromthe direction in which the direct-current voltage is transmitted, andperforming the current control again during a designated period of time,wherein a velocity estimation circuit detects a frequency component thatappears in a current detection value and a phase relationship thereof,estimates the frequency component as a velocity of thealternating-current motor, and employs the phase relationship toestimate a rotational direction of the alternating-current motor both avelocity detector and a voltage detector are not provided, thesensorless vector control method further comprising the step of: whenthe velocity and the rotational direction of the alternating-currentmotor are estimated by providing a direct current instruction for thealternating-current motor, reducing a scanning time period for a currentcontrol process to less than that for a normal control process.
 24. Thesensorless vector control method for an alternating-current motor,according to claim 23, further comprising the steps of: when thevelocity and the rotational direction of the alternating-current motorare estimated by providing a direct current instruction for thealternating-current motor, reducing a scanning period of time for acurrent control process to less than that for a normal control process,as well as increasing a carrier frequency of the power converter. 25.The sensorless vector control method for an alternating-current motor,according to claim 23 or 24, further comprising the steps of: when thevelocity and the rotational direction of the alternating-current motorare estimated by providing a direct current instruction for thealternating-current motor, reducing a scanning period of time for acurrent control process to less than that for a normal control process,as well as employing a current detector that is different from that usedfor the normal control process and that is so sensitive a small currentis detected.
 26. A sensorless vector control apparatus for analternating-current motor, comprising: a power converter, for outputtingpower to an alternating-current motor, and a current controller, forcontrolling a current output by the power converter based on a signalindicating a deviation between a current instruction signal and adetection signal for a current output by the power converter, whereinboth a velocity detector and a voltage detector are not provided,current control is effected by forcibly setting the current instructionsignal to zero so as to reduce to zero a current in thealternating-current motor in a free running state, when the outputvoltage instruction signal, which is calculated by using a currentoutput by the current controller at this time, is lower than anarbitrarily designated voltage level, current control is halted, and adirect current instruction is transmitted at an arbitrary level in anarbitrary direction for a designated period of time, thereafter, acurrent instruction is transmitted at an arbitrary level in a directionwith a phase 180° different from the direction in which thedirect-current voltage is transmitted, and the current control isperformed again during a designated period of time, and a velocityestimation circuit detects a frequency component that appears in acurrent detection value and a phase relationship thereof, estimates thefrequency component as a velocity of the alternating-current motor, andemploys the phase relationship to estimate a rotational direction of thealternating-current motor, the sensorless vector control apparatusfurther comprising: member for reducing a scanning time period for acurrent control process to less than that for a normal control process,when the velocity and the rotational direction of thealternating-current motor are estimated by providing a direct currentinstruction for the alternating-current motor.
 27. The sensorless vectorcontrol apparatus for an alternating-current motor, according to claim26, further comprising: when the velocity and the rotational directionof the alternating-current motor are estimated by providing a directcurrent instruction for the alternating-current motor, member forreducing a scanning period of time for a current control process to lessthan that for a normal control process, as well as increasing a carrierfrequency of the power converter.
 28. The sensorless vector controlmethod for an alternating-current motor, according to claim 26, furthercomprising: when the velocity and the rotational direction of thealternating-current motor are estimated by providing a direct currentinstruction for the alternating-current motor, a current detector forreducing a scanning period of time for a current control process to lessthan that for a normal control process, as well as employing a currentdetector that is different from that used for the normal control processand that is so sensitive a small current is detected.